This invention relates to monolithic blocks having an internal geometry and, more particularly, to a method of constructing such a block (wherein the small size of the internal geometry is unsuitable for conventional molding technology.)
There are situations where it is desired to produce a monolithic block having an internal geometry which is so small that the fine features thereof cannot be produced through conventional molding technology. For example, in my co-pending U.S. patent application Ser. No. 07/337,730, filed Apr. 13, 1989, and assigned to the assignee of this invention, now U.S. Pat. No. 4,906,194, I disclose a high density connector assembly for an integrated circuit chip carrier which includes a stack of metallic plates having apertures which form chambers for holding planar contact members therein. These plates are relatively thin, illustratively having a thickness of 0.010 inch, and a typical aperture is a rectangular slot 0.0055 inch by 0.080 inch. There are many of these apertures, illustratively equally spaced on 0.0150 inch centerlines. The plates are then stacked in alignment to form a block structure, with the stacked apertures forming a plurality of chambers, each of which can accommodate therein a planar contact member. To insulate the plates from the contact members, the plates are coated with an insulating layer of dielectric material. The stack of plates provides a ground shield and return path around each of the contact members to prevent cross-talk therebetween. Preferably, the plates are made of aluminum which is subsequently anodized or otherwise oxidized to provide a relatively thick layer of oxide on all surfaces of the plates.
Although disclosed in connection with a contact socket for a connector assembly, the aforedescribed technique of providing a stack of thin sheets, each with an appropriate geometry representing the dimensions which one would obtain by cross-sectioning a three-dimensional structure in a given plane, has more general application. This technique may be used whenever the fine features of the internal geometry of a desired monolithic block are so small that the traditional technology of molding plastic becomes inadequate due to a limitation of the space between core pins in the mold into which the plastic will flow, provide an adequate packing density, and retain at least some mechanical strength when extracted from the mold.
However, it has been discovered that such structures present an environmental problem in actual use, because the plates stacked together in close proximity, and even under pressure, will have a capillary interface between their surfaces. Such capillary interface will trap and hold moisture. In the case of water in liquid form, the holding is accomplished by surface tension. In the case of vapors or very thin film, the holding is accomplished by osmotic pressure.
In an (electrical connector,) entrapped moisture is detrimental because it can be a medium for ion transport, thereby providing an electrolytic path between contacts, which may have a difference of potential in relation to each other. This will result in a leakage path being provided between the contacts which can possibly result in corrosion and an ultimate failure of the connector assembly. Furthermore, if the plates are made of anodized aluminum, there is the additional problem of porosity which is, if not inherent, at least typical in an aluminum oxide coating. The sealing of such pores has traditionally been accomplished by vacuum impregnation or coating with organic fillers. However, this still leaves the capillary interface.
It is therefore an object of this invention to provide a method for eliminating capillary interfaces and pores between adjacent plates in a stack of plates forming a block having an internal geometry.